The present invention relates to an improved shimable bumper system for use in a compressor variable vane system that fully traps the shim in case of lost screw preload and that has an anti-rotation feature.
The main components of a compressor variable vane system are the stator vanes, vane arms, synchronizing rings, bumpers, linkage system, and the actuator. The vane arms are used to control the incidence angle of the vanes in the compressor of gas turbine engines. The vanes are arranged as a stage set around the circumference of the compressor. The arm attaches to each vane spindle which rotates in a bearing mounted in the compressor case. The set of vanes are actuated by a circumferential synchronizing ring that rotates about the engine axis. The vane arm imparts motion from the synchronizing ring to the vane spindle. The linkage system and actuator imparts motion to the synchronizing ring. The bumper is used to control the concentricity and the deflection of the synchronizing ring throughout this motion by running at a pre-determined operating gap. Currently, thread adjustment and shimable adjustment are used to set this gap at assembly, taking into account the thermal resultant at operating temperature.
One current bumper configuration, shown in FIG. 1, uses thread adjustment to set the bumper gap. The configuration consists of a stud adjuster 10, a metallic bumper 12 with a bonded on composite liner, and a shear lock collar 14. The bumper 12 is anti-rotated via a matched milled feature 16 in the synchronizing ring 18. There are two technical issues with this configuration. The first is that the load path is through the threads which results in thread wear which leads to an increase in bumper gaps. The second issue is the bonding of a composite liner to a metallic bumper housing. Dis-bonding of the composite liner could occur due to loading and thermal cycling. The dis-bond of the liner also leads to an increase of bumper gaps. Increased bumper gaps decrease the synchronizing ring concentricity and increases the synchronizing ring distortion which leads to an increase in vane angle variation and loss in stall margin.
Thus, there is a need for a new bumper configuration.